Page 25
Vent Piping Guidelines
NOTE - Lennox has approved the use of DuraVent
®
manu
factured vent pipe and terminations as an option to PVC.
When using the PolyPro
®
by DuraVent venting system the
vent pipe requirements stated in the unit installation in
struction – minimum & maximum vent lengths, termination
clearances, etc. – apply and must be followed. Follow the
instructions provided with PoyPro by DuraVent venting
system for assembly or if requirements are more restrict
ive. The PolyPro by Duravent venting system must also fol
low the uninsulated and unconditioned space criteria listed
in table 16.
The ML195UH can be installed as either a Non-Direct
Vent or a Direct Vent gas central furnace.
NOTE - In Non‐Direct Vent installations, combustion air is
taken from indoors and flue gases are discharged out
doors. In Direct Vent installations, combustion air is taken
from outdoors and flue gases are discharged outdoors.
Intake and exhaust pipe sizing -- Size pipe according to
tables 13 and 14. Count all elbows inside and outside the
home. Table 13 lists the minimum vent pipe lengths per
mitted. Table 14 lists the maximum pipe lengths permitted.
Regardless of the diameter of pipe used, the standard roof
and wall terminations described in section Exhaust Piping
Terminations should be used. Exhaust vent termination
pipe is sized to optimize the velocity of the exhaust gas as it
exits the termination. Refer to table 17.
In some applications which permit the use of several differ
ent sizes of vent pipe, a combination vent pipe may be
used. Contact Lennox' Application Department for assis
tance in sizing vent pipe in these applications.
NOTE - The exhaust collar on all models is sized to accom
modate 2” Schedule 40 vent pipe. In horizontal applica
tions, any transition to exhaust pipe larger than 2” must be
made in vertical runs of the pipe. Therefore a 2” elbow must
be added before the pipe is transitioned to any size larger
than 2”. This elbow must be added to the elbow count used
to determine acceptable vent lengths. Contact the Applica
tion Department for more information concerning sizing of
vent systems which include multiple pipe sizes.
FIGURE 25
Exhaust Pipe
NOTE - Exhaust pipe MUST be glued to furnace exhaust fittings.
NOTE - All horizontal runs of exhaust pipe must slope back to
ward unit. A minimum of 1/4” (6mm) drop for each 12” (305mm)
of horizontal run is mandatory for drainage.
NOTE - Exhaust piping should be checked carefully to make
sure there are no sags or low spots.
12” ma x
of straight pip
e
Exhaust Pipe
12” Min.
Horizontal
Gas Furnace
TABLE 13
MINIMUM VENT PIPE LENGTHS
ML195UH
MODEL
MIN. VENT LENGTH*
045, 070, 090, 110
15 ft. or
5 ft plus 2 elbows or
10 ft plus 1 elbow
135
*Any approved termination may be added to the minimum length listed.
Use the following steps to correctly size vent pipe diameter.
FIGURE 26
Piping Size Process
1
2
3
4
5
6
Which style termination
being used?
Standard or concentric?
See table 12.
Which needs
most elbows?
Intake or
exhaust?
How many elbows?
Count all elbows inside
and outside house.
Desired pipe size?
2”, 2-1/2”, 3”
Use table 14 or 15 to find
max intake or exhaust pipe
length. Includes all vent
pipe and elbows inside
and outside the house.
What is the altitude of
the furnace installation?
7
What is the
furnace capacity?
045, 070, 090,
110 or 135?
IMPORTANT
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze-ups
and may block the terminations.
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